For the purpose of bearing very fast-rotating shaftless spinning rotors of open-end spinning machines there are special devices which by means of controlled magnetic forces ensure the position as well as the drive of the spinning rotor. Such devices are generally known as active magnetic bearings.
So as to guarantee proper functioning of the active magnetic bearing, it is essential to know the instantaneous position of the spinning rotor in the magnetic field in the active magnetic bearing and also possible changes of this position over time in a three-dimensional rectangular coordinate system with the axes x, y, z. The spinning rotor must be maintained in the required position by the regulatory (control) system on the basis of continuously detected and assessed data about its position, also in order to avoid an accident of the spinning rotor caused by the influence of a possible excessive deflection of the spinning rotor which would lead to all the negative effects following especially from the high speed of the rotation of the spinning rotor, e.g. an accident due to the contact of the spinning rotor with the other parts of the active magnetic bearing.
In the active magnetic bearings in which the height of the spinning rotor approximates the diameter of the spinning rotor there is a problem of correctly recognizing particularly the so-called oscillations of the spinning rotor during its rotation, i.e. variations of the actual rotation axis of the spinning rotor in relation to the theoretical rotation axis of the spinning rotor. The spinning rotor is maintained in a direction of its rotation axis in a required position by the action of the magnetic forces and permanent magnets of the active magnetic bearing, and so possible shifting of the spinning rotor in a direction of the rotation axis of the spinning rotor is corrected completely automatically by the action of these permanent magnets. Up to now in this simple arrangement basically merely radial shifting of the rotation axis of the rotor is detected by appropriately disposed sensors of the spinning rotor, which in essence work on the principle of detecting changes of distance of the monitored area of the spinning rotor from the sensors and subsequently according to these changes correction of the levitation of the spinning rotor is carried out.
Therefore conventional sensors of the spinning rotor usually work in pair arrangement, i.e. in pairs, whereby all the pairs are disposed in one plane along the circumference area of the spinning rotor, where they are capable of detecting radial shifting of the spinning rotor in relation to the theoretical rotation axis. However, in this disposition they are not capable of identifying reliably changes of the position of the spinning rotor caused by the oscillations of the spinning rotor, whereby these possible oscillations are not corrected spontaneously by the action of the magnetic forces of the permanent magnets of the active magnetic bearing.
For the purpose of detecting the oscillations of the rotor, it is possible to apply an arrangement of sensors of the spinning rotor in two parallel sensing planes against the outer circumference of the spinning rotor, i.e. against its cylindrical area. However, this solution is costly and requires additional space for a second, parallel system of sensors, detectors and evaluation circuits. Furthermore, due to the small length of shaftless spinning rotors and due to generally relatively small spinning units with active magnetic bearings in open-end spinning machines, this necessary additional space is not available without a substantial increase in the length of shaftless spinning rotors as well as in the external dimensions of the spinning units.
The goal of the invention is to eliminate or at least reduce the shortcomings of the background art, particularly to improve possibilities of detecting the position of a shaftless spinning rotor in a spinning unit of an open-end spinning machine.